Pneumatic head-actuating system having automatic control for reading and writing through heads

ABSTRACT

A pneumatic system for controlling the relative position of electromagnetic heads with respect to a magnetic disc recording surface. A source of fluid pressure is supplied through a first valve means to the input port of a pressure regulator and to the input port of a second valve means. Pressure emanating from the output port of the regulator is applied to electromagnetic heads which causes them to move from a first to a second position relative to the magnetic disc surface. Pressure emanating from the output port of the second valve means is supplied to a pneumatic switch for enabling or disabling electrical circuit means which reads or writes information from the magnetic recording disc through the magnetic heads. The second valve means has a first time delay corresponding to the rate of fluid flow from its input to output port which insures the enabling of the electrical circuit by the pneumatic switch only after the heads have moved into their second position, and has a second time delay, shorter than the first time delay, corresponding to the rate of fluid flow from its output to input port which insures the disabling of the electrical circuit by the pneumatic switch before the heads commence movement from their second position back to their first position.

United States Patent Gyi [ Feb. 8, 1972 [54] PNEUMATIC HEAD-ACTUATING SYSTEM HAVING AUTOMATIC CONTROL FOR READING AND WRITING THROUGH HEADS K0 K0 Gyi, Thousand Oaks, Calif.

Burroughs Corporation, Detroit, Mich.

Feb. 9, 1970 [72] inventor:

Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS 2,716,997 9/1955 Crookston ..137/513.3 3,169,548 2/1965 McIntosh Primary ExaminerBemard Konick Assistant Examiner-J. Russell Goudeau Attorney-Christie, Parker & Hale [57] ABSTRACT A pneumatic system for controlling the relative position of electromagnetic heads with respect to a magnetic disc recording surface. A source of fluid pressure is supplied through a first valve means to the input port of a pressure regulator and to the input port of a second valve means. Pressure emanating from the output port of the regulator is applied to electromagnetic heads which causes them to move from a first to a second position relative to the magnetic disc surface. Pressure emanating from the output port of the second valve means is supplied to a pneumatic switch for enabling or disabling electrical circuit means which reads or writes information from the magnetic recording disc through the magnetic heads. The second valve means has a first time delay corresponding to the rate of fluid flow from its input to output port which insures the enabling of the electrical circuit by the pneumatic switch only after the heads have moved into their second position, and has a second time delay, shorter than the first time delay, corresponding to the rate of fluid flow from its output to input port which insures the disabling of the electrical circuit by the pneumatic switch before the heads commence movement from their second position back to their first position.

15 Claims, 9 Drawing Figures lk 72 III PATENTEUFEB 8 I972 3.641.527

sum 3 OF 3 PNEUMATIC HEAD-ACTUATING SYSTEM HAVING AUTOMATIC CONTROL FOR READING AND WRITING THROUGH HEADS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to storage systems having electromagnetic heads which float on a thin film of air adjacent a moving magnetic recording surface for reading and writing on the recording surface. More specifically, the invention relates to a pneumatic system for controlling the relative position of the electromagnetic heads with respect to a magnetic recording surface.

2. Description of the Prior Art Fluid pressure systems of the past utilize an air compressor to supply air pressure to a solenoid valve which controls the application of air pressure to the input port of a pressure regulator and to a pneumatic switch. Air pressure from the output port of the regulator is uniformly supplied to a head support through a flow control valve for causing the electromagnetic heads to uniformly move from a first to a second position relative to the magnetic disc recording surface. The pneumatic switch enables or disables an electrical circuit which reads from or writes to the recording disc surface through the heads. When air pressure of a preselected value is supplied to the switch from the solenoid valve, the electrical circuit is enabled to read or write. When the solenoid valve cuts off the air pressure, and the pressure supplied to the switch thereby drops to a preselected value, the electrical circuit is disabled from reading or writing.

A problem was discovered with such prior art system. The electrical circuit was being enabled by the pneumatic switch before the electromagnetic heads reached their second position, such position corresponding to the so-called flying height above the magnetic disc surface at which the floating heads optimumly perform read and write functions. During the period of time that the electrical circuit is actuated before the head reached its flying height (second position), erroneous read and write data was obtained. Correspondingly, when the solenoid valve cuts off the supply of air pressure to the switch, the electrical circuit is disabled after the commencement of movement of the heads from their second position back to their first, norma nonflying position and, as a result, erroneous data is obtained.

A solution was attempted for the above problem. The pneumatic switch was moved from the primary-input side of the pressure regulator to the secondary-output side. It was felt that, with the switch so positioned, the same amount of pressure that causes the heads to reach their flying height would also cause the switch to enable the electrical circuit. In other words, reaching of the flying height and enabling of the electrical circuit would occur simultaneously. This, however, does not take into account the time it takes for the actual switching operation to occur once the pressure, which causes the heads to reach their flying height, is supplied to the switch. In other words, erroneous data is still obtained during this brief time interval.

The above-attempted solution was found to be extremely impractical and ineffectual during the retract cycle of the heads, i.e., the time period during which the heads move from their second back to their first position. By virtue of the inherent hysteresis of the pneumatic switch and its location on the secondary-output side of the regulator, it caused the electrical circuit to deactuate only after the secondary pressure supply to the switch decreased a significant amount. The heads, on the other hand. instantaneously started to retract as soon as the secondary pressure started to decrease. The result is a substantial duration of time during which the heads are not at their flying height (second position), but that the electrical circuit is still actuated. The errors during this time are likewise substantial. The solution, therefore, proved ineffectual to eliminate, as opposed to reduce, read and write data errors.

SUMMARY OF THE INVENTION This invention entirely and completely eliminates the erroneous data problem of past fluid pressure systems, hereinabove described, through the addition of certain valve means coupling the output port of the solenoid valve to the pneumatic switch, the latter being located on the primaryinput side of the pressure regulator. Such valve means is fabricated and designed such that fluid pressure flowing therethrough from the output port of the solenoid valve to the pneumatic switch will cause the switch to enable the electrical circuit to read or write from or to, respectively, the magnetic recording surface, through the electromagnetic heads, only after a time period corresponding to a first time delay, such period of time insuring that the pneumatic switch will enable the electrical circuit means only after the heads have reached their second position (flying-height). Additionally, a second time delay, shorter than the first, is inherent in the fabrication of the valve means and operates, upon the cessation of fluid pressure supplied to it from the solenoid valve, and thus during the return flow of fluid pressure from the output to input port of the valve means, to insure that the pneumatic switch disables the electrical circuit prior to the commencement of the retract cycle of the heads (hereinabove defined).

In another aspect of the invention, such valve means comprises a chamber portion formed between its input and output ports, and a pair of interconnected disc-shaped members located within the chamber, each of the pair having a plurality of apertures, at least one aperture from each of the pair being in alignment and at least one aperture from each being in nonalignment.

In yet another aspect of the invention, the total area of the aligned apertures is smaller than the total area of the nonaligned apertures thereby making the first time delay greater than the second time delay.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 represents a flow diagram of a prior art pneumatic system;

FIG. 2 is a graphical representation of the fly cycle of the prior art pneumatic system of FIG. I; i

FIG. 3 represents a flow diagram of another prior art pneumatic system;

FIG. 4 is a graphical representation of the fly cycle of the prior art pneumatic system of FIG. 3;

FIG. 5 is a graphical representation of the retract cycle of the prior art pneumatic system of FIG. 3;

FIG. 6 represents a flow diagram of the pneumatic system according to the present invention;

FIG. 7 is a graphical representation of the fly cycle of the pneumatic system of FIG. 6;

FIG. 8 is a graphical representation of the retract cycle of the pneumatic system of FIG. 6; and

FIG. 9 is a detailed cross-sectional view of the pneumatic time delay shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT The prior art pneumatic system of FIG. 1 is used to control the relative position of the electromagnetic heads 10 with respect to a rotating magnetic disc surface 12. The heads 10 are constructed for and float on a thin film of air created adjacent the rotating disc surface 12. A pneumatic actuating mechanism 14 actuates the heads 10 into and out of a floating position with respect to the disc 12. The exact construction of the head and its pneumatic actuating mechanism 14 may be in the form disclosed in U.S. Pat. No. 3,320,599, although the invention is not limited thereto.

Air compressor 16 supplies air pressure through filter l8 and manifold 20 to the first port 22 of solenoid valve 24, which also has second and third ports 26 and 28, respectively. Third port 28 is always exposed to atmospheric pressure. The valve 24 may be constructed in any one of a number of different arrangements well known in the pneumatic valve art. Briefly, means 30 are included in the solenoid valve 24 for alternatively establishing a flow path either between ports 22 and 26 or between ports 26 and 28 (thereby establishing atmospheric pressure at port 26). When the heads are sought to be moved into a position for reading or writing, means 30 establishes a flow path from port 22 to port 26 thereby allowing air pressure from compressor 16 to flow toward the input port 32 of pressure regulator 34. The air pressure on the input port side of the pressure regulator 34 will be hereinafter referred to as the primary pressure, P,,.

Air pressure emanating from output port 36 of the pressure regulator, and hereinafter referred to as the secondary pressure, P,, is applied through flow control valve 38 to the head actuating mechanism 14. Flow control valve 38 operates to restrict the flow of secondary pressure supplied to mechanism 14 in order to obtain an even and uniform movement of the heads from the first to the second position (hereinafter defined) relative to the magnetic disc surface 12.

It will help, at this point, to define and establish certain terms for use hereinafter. The first position of the electromagnetic heads refers to the situation when no secondary pressure is supplied to head actuating mechanism 14. This first position, therefore, corresponds to the normal nonflying position of the electromagnetic head relative to the surface of the magnetic disc. The second position of the electromagnetic heads corresponds to the distance above the magnetic disc at which the floating head lands" and then optimurnly performs read and write functions, as hereinbefore described. Such second position will be hereinafter referred to as the flying height of the electromagnetic head. Movement of the electromagnetic head from its first to its second position shall be hereinafter referred to as the flying cycle of the head. Movement of the electromagnetic head from its second position back to its first position will be hereinafter referred to as the retract cycle of the electromagnetic head.

A unidirectional check valve 40 is connected between the output port 26 of solenoid valve 24 and the input to the head actuating mechanism 14 such that its uninhibited direction of flow is from mechanism 14 to solenoid valve 24, i.e., the return flow of the secondary air pressure during the retract cycle of the heads. Valve 40, therefore, will not pass secondary air pressure during the fly cycle, such pressure passing through regulator 34 and flow control valve 38 to mechanism 14. The use of valve 40 is significant when considering the problem overcome by the present invention (to be fully explained below). Rapid retraction of the heads is desirable for numerous reasons, e.g., a head accidentally touches the magnetic disc surface and further damage is to be avoided by retracting such head. In this regard, valve 40 greatly speeds up the retract cycle of the heads relative to the fly cycle. This is done by bypassing the regulator 34 and control valve 38 and supplying the return flow of secondary pressure directly to solenoid valve 24. The complete operation of the entire system will be fully explained hereinbelow.

A pneumatic switch 42 is connected to the second port 26 of solenoid valve 24. The switch is responsive to the application of a preselected amount of primary air pressure and, when actuated, enables electrical circuit 44 to read from or write to magnetic recording surface 12 through the electromagnetic heads 10. In the embodiment of FIG. 1, as well as that of FIGS. 3 and 6, the electrical circuit 44 includes electrical read and write circuits for magnetic heads and a disc file control unit for control of the reading and writing operations, such devices being well known in the disc file art. Pneumatic switch 42 has two states: the first is responsive to the application of a preselected amount of primary air pressure for enabling the electrical circuit; and the second is responsive to the cessation of the application of primary air pressure for disabling the electrical circuit from reading or writing.

In operation, and with reference to the prior art pneumatic system of FIG. 1, air pressure is supplied from compressor 16 through filter 18 and manifold to solenoid valve 24. Solenoid valve 24 is normally closed, i.e., means 30 normally establishes a path from port 28 to port 26, thereby maintaining the latter at atmospheric pressure, and thereby prohibiting the flow of air pressure from compressor 16 to the input port 32 of pressure regulator 34, the pneumatic switch 42, and check valve 40. Correspondingly, the electromagnetic heads are in their normal nonflying position. When it is desired to actuate the heads into their flying-height" position relative to the magnetic disc surface 12, the solenoid valve 24 is opened, i.e., means 30 establishes a path from port 22 to port 26. In this condition, primary air pressure from compressor 16 is supplied to the input port 32 of pressure regulator 34, to the pressure-sensitive switch 42, and to check valve 40. As has been stated before, the latter will not pass primary air pressure. Pneumatic switch 42, however, actuates electrical circuit 44 to enable it to receive read or send write information to the magnetic disc surface 12 through the heads 10. In order for the electrical circuit 44 to do this, the electromagnetic heads must be at their desired flying height position. This is eventually accomplished by the secondary pressure which is emitted from the output port 36 of pressure regulator 34. Such secondary pressure is uniformly supplied in a specific preselected quantity through flow control valve 38 to head actuating mechanism 14 causing the electromagnetic heads to move to their flying height" position.

It would seem, therefore, that the above-described prior an system functions perfectly and without any problems during the flying cycle of the heads. This, however, is not the case when considering the graphical representation of the fly cycle shown in FIG. 2 which contains two graphs. The lower graph is a plot of the primary pressure P,,, versus time, and the upper graph is a plot of the secondary pressure P,,, versus time. On the lower graph, t,, represents the primary pressure rise time, i.e., the time it takes the primary pressure to reach its maximum condition. The exact time at which the primary pressure reaches such condition is shown by point A on the lower graph. On the upper graph, t, represents the secondary pressure rise time corresponding to the time it takes for the heads to begin to fly at their flying height after valve 24 is turned on. Point B on the upper graph represents the exact pressure and time at which the secondary pressure increases to the extent of causing the heads to fly at their flying height. Carrying a vertical line down from point B through the time axis of the lower graph, it can be seen that the pneumatic switch 42 has enabled the electrical circuit 44 to read or write, represented by point C, at a time, represented by 1-,, prior to the time that the heads reach their flying height, represented by point B. Various read and write errors are in evidence during the time 1-,.

In a previous attempt to cure the above-mentioned errors an alternative prior art embodiment was designed and is shown in FIG. 3. The only difference between this embodiment and the embodiment shown in FIG. 1 is that the pneumatic switch 42 is now coupled to the secondary-output side of pressure regulator 34. This was done for the purpose of attempting to synchronize the enabling of electrical circuit 44 by pneumatic switch 42 and the movement of the electromagnetic heads into their second position (flying height). Such was not the case, however, because the time it takes the pneumatic switch to actually perform its switching operation was not accounted for. The result of such nonaccounting will be seen with reference to the description of FIG. 4 below. The embodiment of FIG. 3 was extremely inefficient and ineffective during the retract cycle of the electromagnetic heads. Due to the inherent hysteresis in pneumatic switch 42, and the fact that such switch is located on the secondary-output side of pressure regulator 34, the heads 10 actually moved away from the magnetic disc surface 12 prior to the disabling of the electrical circuit 44 by the pneumatic switch 42. In other words, when solenoid valve 24 cut off the supply of primary air pressure through pressure regulator 34, the secondary air pressure at actuating mechanism 14 started to decrease because atmospheric pressure existed in the primary-input side due to the establishment, by means 30, of a flow path from port 28 (at atmospheric pressure) to port 26 of solenoid valve 24. correspondingly, the heads started to retract. The pneumatic switch 42, by reason if its inherent hysteresis, did not disable the electrical circuit 44 until a time after the commencement of retraction of the electromagnetic heads from their second flying height position back to their first nonflying position.

FIGS. 4 and 5 are graphical representations of the fly and retract cycles, respectively, of the alternative prior art embodiment shown in FIG. 3. In FIG. 4, t, represents the secondary pressure rise time, as hereinbefore defined. Point D represents the position where the electromagnetic heads are flying at their flying height. Point E represents the point in time at which the secondary pressure has increased to the point at which it causes pneumatic switch 42 to enable electrical circuit 44. Time delay, 1 therefore, results and is indicative of the period of time during which the electrical circuit 44 is enabled but which the electromagnetic heads have not yet reached their proper flying height. Read and write errors occurred during such period. The heads are retracted from the surface 12 by closing solenoid valve 34 thereby establishing atmospheric pressure at second port 26, thereby prohibiting the flow of primary pressure to pressure regulator 24. Under these conditions, secondary pressure will rapidly decrease, due to return flow through check valve 40, with the corresponding commencement of retraction of the heads away from the disc surface from their flying height back to their first nonflying position. Point F in the graph of FIG. 5 shows the point at which solenoid valve is closed and the heads commence their retraction away from the disc surface. By reason of the inherent hysteresis of pressure switch 42, and since it is located on the secondary-output side of the pressure regulator, it will cause the deactuation of the electrical circuit means 44 at a point in time after the heads 10 have commenced their movement away from the disc surface 12. Such point is represented by G on the graph of FIG. 5. A time, 1 is, therefore, established and is indicative of the period of time during which the electrical circuit 44 is still enabled but the heads are no longer at their proper flying height. As before, read and write errors occur during this period of time.

FIG. 6 is a representative embodiment of the pneumatic system according to the invention. The major and significant difference between this system and that of the prior art shown in FIG. 1 is the addition and use of a pneumatic time delay 46 coupling the second port 26 of the solenoid valve 24 to the pneumatic switch 42. Pneumatic time delay 46 has two unique and different time delays, one being responsive to the application of primary pressure supplied thereto and the other being responsive to the cessation of primary pressure supplied thereto. Such time delays are preselected in a manner which will be hereinafter described. The first time delay is preselected such that, during the fly cycle of the electromagnetic head, sufficient primary pressure to cause the enabling of electrical circuit 44 will be delivered to pneumatic switch 42 only after the electromagnetic heads have arrived at their flying height." Furthermore, the second time delay is preselected such that, during the retract cycle of the electromagnetic heads, primary pressure built up at the pneumatic switch 42 will decrease swiftly causing the switch to disable the electrical circuit prior to the commencement of movement of the heads away from the disc surface from their flying height back to their nonflying position.

Graphical representations of the operative effect of such first and second preselected time delays are shown in FIGS. 7 and 8, which, respectively, represent the fly cycle and retract cycle of the electromagnetic heads. Point H in FIG. 7 represents a point corresponding to the time at which the secondary pressure is sufficient to cause the electromagnetic heads to fly at their proper flying height. Once again, t, represents this time interval. Point I represents the point in time at which the primary pressure increases sufficiently to cause the pneumatic switch 42 to enable the electrical circuit 44. Time, 7 is the period of time between the time when the heads are flying at their proper flying height and the time the pneumatic switch enables the electrical circuit 44. The first preselected time delay, therefore, makes sure that the electrical circuit 44 is enabled only after the electromagnetic heads are at their proper flying height.

In the retract cycle of the electromagnetic heads, and with reference to FIG. 8, point .I represents the point in time corresponding to the commencement of retraction of the elec tromagnetic heads away from their flying height back to their nonflying position. Point K, occurring at a time prior to point J, indicates disabling of the electrical circuit 44 by pressure switch 42. Time, r therefore, is established which represents the period of time after the electrical circuit is disabled by switch 42 during which the heads are still at their flying height. The second preselected time delay, therefore, makes sure that the electrical circuit 44 is disabled prior to the commencement of retraction of the heads 10 from the disc surface 12.

The novel fabrication of pneumatic time delay 46 will now be fully and completely described with reference to FIG. 9. Basically, the pneumatic time delay consists of the combination of an accumulator and a flow control and check valve. Accumulator 24 is formed by mounting a metallic cover 50 on a metallic base member 52 and sealing the interface therebetween by means of O-ring 54. Cover 50 forms a pressure chamber 56 with the mounting base 52. Mounting base 52 is fabricated such that primary pressure input and output ports 58 and 60, respectively, are formed therein. A flow control and check valve assembly is mounted in the path of the flow of the air between the input port 58 and output port 60. The flow control and check valve consists of a metallic disc member 64 containing a plurality of apertures 66 of equal size (only one being shown) An aperture 68 of much smaller area than apertures 66 is also contained in metallic disc member 64. Metallic disc member 64 is fixedly mounted to one side of a diaphragm member 70 by means of bushing 72, thus forming an assembly 65. Diaphragm 70 is fabricated of a resilient material, such as cloth impregnated with silicon rubber, and is configured as a disc with the exact same diameter as metallic disc member 64. The input port 58 has an annular shaped portion terminating at a ring-shaped shoulder 61. The assembly 65 (disc member 64 and diaphragm 70) seats on a ring-shaped bushing 62 which is mounted on the ring-shaped shoulder 61. The bushing forms a seal between diaphragm 70'and shoulder 61. Ring-shaped seal 67 is further provided in order to form a seal between disc-shaped member 64 and shaft 77 of bolt 76.

Contained in the diaphragm are a plurality of apertures 74 of equal size and shape as the plurality of apertures 66 in metallic disc member 64 (only one of such plurality of apertures 74 being shown). It should be understood that the invention is not limited to a construction where apertures 66 and 74 are of the same size and shape. Metallic disc 64 and diaphragm 70 are mounted such that the only apertures from both that are in alignment are the apertures 68 of smaller area contained in metallic disc 64 and one of the apertures 74 of the diaphragm member 70. Bushing 72 is mounted about a bolt 76 disposed within shaft 77 which, with nut 78, is used to mount the entire check and flow control valve assembly to the base member 52 in sealing relationship with input port 58. In

other words, nut 78 is used to tighten the check and flow control valve assembly 65 into frictional engagement with seal 62 and seal 67 such that its positional relationship will not change responsive to changes in pressure at either input port 58 or output port 60. With the metallic disc member 64 and diaphragm 70 frictionally and positionally mounted as above described, check valves are established at apertures 66 and 74 and a flow control valve is established at aperture 68.

In other words, aperture 68 will restrict the flow of primary air pressure into chamber 56 when such pressure is greater than the pressure in the chamber and thus at output port 60. Aperture 68 and its corresponding aligned aperture 74, represent the only path that such primary pressure can take into the chamber since resilient diaphragm 70 will act to seal off all of the nonaligned apertures 66 and 74. When the chamber pressure is greater than the primary pressure, e.g., when solenoid valve 24 cuts off supply of primary pressure thus reducing it to atmospheric pressure, resilient diaphragm 70 will deflect downward into the input port 58 and thus allow the chamber pressure to escape through all of the apertures in both disc-shaped members.

In operation, primary air pressure supplied through solenoid valve 24 (FIG. 6) enters chamber 56 through input port 58. Such primary pressure, being greater than the atmosphere pressure in the chamber, will flow toward the check and flow control valve assembly which is frictionally mounted in sealing relationship with sea] 62 and the input port 58 by means of seal 67, nut 78 and bolt 76 as above described. The primary air pressure will attempt to pass through the combination metallic disc and diaphragm members into the chamber 56, since it is at atmospheric pressure. By reason of the positional relationship of the disc member 64 with resilient diaphragm member 70, as hereinabove described, such primary pressure will flow only through the flow control valve established by aperture 68 located in disc member 64. Primary pressure will not flow through any of the apertures 66 because none of them are aligned with the apertures 74. In other words, diaphragm 70 will seal off all of the aperture-check valves 66 when the primary air pressure at input port 58 is greater than the air pressure located in chamber 56. It can be seen, therefore, that the chamber pressure will slowly build up and thus at output port 60, and will cause pressure switch 42, coupled to output port 60, to enable electrical circuit means 44. A first time delay is thus established corresponding to the amount of time necessary for the pressure, passing through the flow control aperture 68 to build up sufficiently to cause pressure switch 42 to enable the electrical circuit 44. Such time delay can be preselected merely by fabricating the flow control aperture 68 of different areas, the smaller the area the greater the time delay and by adjusting the actuation pressure value of switch 42. When it is desired to retract the heads from the disc, solenoid valve 24 cuts ofi" the supply of primary air pressure to the input port 58 of accumulator 48. The pressure at input port 58 will, therefore, return to atmospheric pressure because means 30 of solenoid 24 established a flow path between ports 26 and 28 (the latter being at atmospheric pressure). Since the chamber pressure at output port 60 is greater than atmospheric pressure, it will seek to flow back through the chamber to the input port 58. The pressure at the output port 60 thereby decreases rapidly since it flows through the large plurality of apertures 66 in metallic disc 64 and then through the large plurality of apertures 74 in resilient diaphragm 70, the diaphragm deflecting downward to allow such passage. A second faster time delay is thus established corresponding to the time it takes the chamber pressure to flow through apertures 66 and 74 in sufficient amounts to render the pressure at output port 60 small enough to cause pressure switch 42 to disable the electrical circuit 44. It should be noted that some of the chamber pressure will flow back through the flow control aperture 68 and then through apertures 74 to the primary-input port side of accumulator 48. This flow, however, is de minimus when considering the pressure flowing through apertures 66 and then through apertures 74 to the input port 58. The second time delay can be preselected merely by fabricating apertures 66 and 74 of a specific area. In other words, the larger the diameter of apertures 66 and 74 the faster the secondary pressure at output port 60 will decrease by flowing back therethrough to the input port side of the accumulator. The preferred embodiment shown in FIG. 9, with the total opening area of apertures 66 and 74 being larger than that provided by the flow control aperture 68, will necessarily make the second time delay substantially less than the first time delay. As has been pointed out with regard to FIGS. 7 and 8, the time delays are such that during the fly cycle"; of the electromagnetic heads, the electrical circuit 44 is enabled only after the heads reach their flying height; whereas during the retract cycle" of the electromagnetic heads, the electrical circuit is disabled rapidly prior to the commencement of movement of the head from its flying height back to its nonflying position. Therefore, even though the heads are rapidly retracted by means of the unidirectional valve 40, the electrical circuit 44 is even more rapidly disabled at a time prior to the commencement of rapid retraction.

What is claimed is:

I. In a storage system having a magnetic recording surface; electromagnetic heads for reading and writing on the recording surface; pneumatic actuating means for actuating the heads into a reading position with respect to the surface; a pressure regulator coupled to the pneumatic actuating means, and having an input port; first valve means having an output coupled to the input port of the regulator for applying first and second pressures to the regulator for actuating and deactuating the heads to a reading position; controllable electrical circuit means for reading and writing through the heads; and a pneumatic actuated switch coupled to the electrical circuit having first and second states for enabling and disabling reading and writing by the electrical circuit means; the improvement comprising:

second valve means having an input port coupled to the output of the first valve means and an output port coupled to the pneumatic switch, the second valve means having a first, relatively longer time delay for the application of the first pressure to the pneumatic switch which enables the heads to be actuated into'a reading position before the electrical circuit is enabled, and the second valve means having a second, relatively shorter time delay for the application of the second pressure to the pneumatic switch which enables the pneumatic switch to change states and disable reading and writing in the electrical circuit prior to the moving of the heads out of a reading position.

2. A storage system according to claim 1 comprising a unilateral fluid flow check valve coupled around the regulator for bypassing the regulator when the second pressure is applied to the regulator.

3. A storage system according to claim 1 wherein the valve means comprises an accumulator chamber adjacent the outlet port for accumulation of gas for gradually building a sufficient pressure to actuate the pneumatic switch.

4. A storage system according to claim I wherein the second valve means comprises a passage for the flow of fluid between the input and output ports thereof and a seat separating the input and output ports, a pair of disc-shaped members on the seat, the disc-shaped members being connected together and each having at least one nonaligned passage therethrough and each having at least one aligned passage therethrough, a first one of the disc-shaped members being comprised of a resilient material which deforms away from a second disc-shaped member to permit fluid flow through the nonaligned passages from the second to the first member and seals off the nonaligned passages to cause fluid flow only through the aligned passages from the first to the second member; and a chamber adjacent the outlet port for accumulation of gas.

5. A storage system according to claim 4 wherein the aligned passage has a smaller effective area for the flow of fluid than the nonaligned passages.

6. A storage system according to claim 4 wherein the aligned and nonaligned passages comprise a circular opening through each of the disc-shaped members.

7. A storage system according to claim 4 wherein the first disc-shaped member is in abutting relationship to the seat and the second disc shaped member is a rigid member positioned on the opposite side of the first disc-shaped member from the seat.

8. A storage system according to claim 7 comprising means for clamping the center of the first and second disc-shaped members together.

9. A storage system according to claim 8 comprising means for exerting a force at the center of the disc-shaped members causing the outer edges thereof to form a friction and fluidtight connection with the seat.

10. In a pneumatic system, for controlling the position of electromagnetic heads relative to a magnetic recording surface, comprising:

first valve means having first, second and third ports, and containing means for alternatively providing a flow path either between the first and second ports or between the second and third ports;

a pressure regulator having an input port and an output means supplying fluid pressure to the first port of the first valve means;

means coupling the second port of the first valve means to the input port of the pressure regulator;

means coupling the output of the pressure regulator to the electromagnetic heads such that, responsive to the flow of fluid pressure from the output port of the pressure regulator, the heads will move from a first to a second position relative to the magnetic disc recording surface, and such that, responsive to the cessation of fluid pressure from the output port of the pressure regulator, the heads will return to their first position;

electrical circuit means for reading or writing information to or from, respectively, the magnetic-disc recording surface through the electromagnetic heads; and

' at least one aperture from each of the pair of disc-shaped members being in nonalignment; and wherein a sufficient part of the chamber portion is between the disk-shaped members and the outlet port for forming a pressure accumulator volume into which gas must flow from the inlet port for gradually building a sufficient pressure to actuate the pneumatic switch.

a pneumatic switch having first and second states for enabling or disabling, respectively, the reading or writing by the electrical circuit means; the improvement comprising:

second valve means comprising:

an input port adapted to receive fluid pressure, an output port coupled to the pneumatic switch, the

second valve means having a first, relatively longer time delay, corresponding to the rate of fluid flow from the input port to the output port, which insures the enabling of the electrical circuit means by the pneumatic switch after the heads reach their second position, and

a second, relatively shorter time delay, corresponding to the rate of fluid flow from the output port to the input port, which insures the disabling of the electrical circuit means by the pneumatic switch before the heads com mence movement away from their second position back to their first position.

11. The pneumatic system of claim 10 in which the second valve means further comprises:

a chamber portion formed between the input and output ports;

a pair of interconnected disc-shaped members located within the chamber, each of the pair of disc-shaped members having a plurality of apertures, at least one aperture from each of the pair of disc-shaped members being in alignment and at least one aperture from each of the pair of disc-shaped members being in nonalignment, and wherein a sufficient part of the chamber portion is between the disc-shaped members and the outlet port for forming a pressure accumulator volume into which gas must flow from the inlet port for gradually building a sufficient pressure to actuate the pneumatic switch.

12. The pneumatic system of claim 11 in which the pair of disc-shaped members are disposed in sealing relationship with the input port of the second valve means.

13. The pneumatic system of claim 12 in which only one aperture from each of the pair of disc-shaped members is in ali ment.

4. The pneumatic system of claim 12 in which a first of the pair of disc-shaped member is composed of resilient material, the first disc-shaped member deforming away from the second disc-shaped member when fluid seeks to flow from the second to the first disc-shaped member thereby allowing fluid to flow through all of the apertures in both disc-shaped members, and the first disc-shaped member sealing off the nonaligned apertures when fluid seeks to flow from the first to the second discshaped member thereby allowing fluid to flow through only the aligned apertures in the disc-shaped members.

15. The pneumatic system of claim 14 in which the total area of the nonaligned apertures is greater than the total area of the aligned apertures thereby making the first time delay greater than the second time delay.

zg gg UNITED STATES PATENT OFFICE CERTIFICATE CF CORRECTION Patent NO. 3,641,527 Dated February a, 1972 Inventor(s) K0 K0 Gyi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 34 "flying" should be "fly" I Col. 4, line 29 "flying" should be "fly" Col. 5, line 4 v "if" should be "of" Col. 9, line 27 delete paragraph beginning "at least one I aperture" and ending "the pneumatic switch" Col'.l0, line 31 "member should be "members" Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Atte sting Officer Commissioner of Patents g gi UNITED STATES PATENT OFFICE CERTIFIQATE 9F QORRECTION Patent No. 3,641,527 Dated February 8, 1972 Inventor(s) K0 K0 Gyi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 34 "flying" should be "fly" Col. 4, line 29 "flying" should be "fly" Col. 5, line 4 "if" should be "of" Col. 9, line 27 delete paragraph beginning "at least one I aperture" and ending "the pneumatic switch" (1011,10, line 31 "member" should be "members" Signed and sealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Atte sting Officer Commissioner of Patents 

1. In a storage system having a magnetic recording surface; electromagnetic heads for reading and writing on the recording surface; pneumatic actuating means for actuating the heads into a reading position with respect to the surface; a pressure regulator coupled to the pneumatic actuating means, and having an input port; first valve means having an output coupled to the input port of the regulator for applying first and second pressures to the regulator for actuating and deactuating the heads to a reading position; controllable electrical circuit means for reading and writing through the heads; and a pneumatic actuated switch coupled to the electrical circuit having first and second states for enabling and disabling reading and writing by the electrical circuit means; the improvement comprising: second valve means having an input port coupled to the output of the first valve means and an output port coupled to the pneumatic switch, the second valve means having a first, relatively longer time delay for the application of the first pressure to the pneumatic switch which enables the heads to be actuated into a reading position before the electrical circuit is enabled, and the second valve means having a second, relatively shorter time delay for the application of the second pressure to the pneumatic switch which enables the pneumatic switch to change states and disable reading and writing in the electrical circuit prior to the moving of the heads out of a reading position.
 2. A storage system according to claim 1 comprising a unilateral fluid flow check valve coupled around the regulator for bypassing the regulator when the second pressure is applied to the regulator.
 3. A storage system according to claim 1 wherein the valve means comprises an accumulator chamber adjacent the outlet port for accumulation of gas for gradually building a sufficient pressure to actuate the pneumatic switch.
 4. A storage system according to claim 1 wherein the second valve means comprises a passage for the flow of fluid between the input and output ports thereof and a seat separating the input and output ports, a pair of disc-shaped members on the seat, the disc-shaped members being connected together and each having at least one nonaligned passage therethrough and each having at least one aligned passage therethrough, a first one of the disc-shaped members being comprised of a resilient material which deforms away from a second disc-shaped member to permit fluid flow through the nonaligned passages from the second to the first member and seals off the nonaligned passages to cause fluid flow only through the aligned passages from the first to the second member; and a chamber adjacent the outlet port for accumulation of gas.
 5. A storage system according to claim 4 wherein the aligned passage has a smaller effective area for the flow of fluid than the nonaligned passages.
 6. A storage system according to claim 4 wherein the aligned and nonaligned passages comprise a circular opening through each of the disc-shaped members.
 7. A storage system according to claim 4 wherein the first disc-shaped member is in abutting relationship to the seat and the second disc-shaped member is a rigid member positioned on the opposite side of the first disc-shaped member from the seat.
 8. A storage system according to claim 7 comprising means for clamping the center of the first and second disc-shaped members together.
 9. A storage system according to claim 8 comprising means for exerting a force at the center of the disc-shaped members causing the outer edges thereof to form a friction and fluidtight connection with the seat.
 10. In a pneumatic system, for controlling the position of electromagnetic heads relative to a magnetic recording surface, comprising: first valve means having first, second and third ports, and containing means for alternatively providing a flow path either between the first and second ports or between the second and third ports; a pressure regulator having an input port and an output port; means supplying fluid pressure to the first port of the first valve means; means coupling the second port of the first valve means to the input port of the pressure regulator; means coupling the output of the pressure regulator to the electromagnetic heads such that, responsive to the flow of fluid pressure from the output port of the pressure regulator, the heads will move from a first to a second position relative to the magnetic disc recording surface, and such that, responsive to the cessation of fluid pressure from the output port of the pressure regulator, the heads will return to their first position; electrical circuit means for reading or writing information to or from, respectively, the magnetic-disc recording surface through the electromagnetic heads; and at least one aperture from each of the pair of disc-shaped members being in nonalignment; and wherein a sufficient part of the chamber portion is between the disk-shaped members and the outlet port for forming a pressure accumulator volume into which gas must flow from the inlet port for gradually building a sufficient pressure to actuate the pneumatic switch. a pneumatic switch having first and second states for enabling or disabling, respectively, the reading or writing by the electrical circuit means; the improvement comprising: second valve means comprising: an input port adapted to receive fluid pressure, an output port coupled to the pneumatic switch, the second valve means having a first, relatively longer time delay, corresponding to the rate of fluid flow from the input port to the output port, which insures the enabling of the electrical circuit means by the pneumatic switch after the heads reach their second position, and a second, relatively shorter time delay, corresponding to the rate of fluid flow from the output port to the input port, which insures the disabling of the electrical circuit means by the pneumatic switch before the heads commence movement away from their second position back to their first position.
 11. The pneumatic system of claim 10 in which the second valve means further comprises: a chamber portion formed between the input and output ports; a pair of interconnected disc-shaped members located within the chamber, each of the pair of disc-shaped members having a plurality of apertures, at least one aperture from each of the pair of disc-shaped members being in alignment and at least one aperture from each of the pair of disc-shaped members being in nonalignment, and wherein a sufficient part of the chamber portion is between the disc-shaped members and the outlet port for forming a pressure accumulator volume into which gas must flow from the inlet port for gradually building a sufficient pressure to actuate the pneumatic switch.
 12. The pneumatic system of claim 11 in which the pair of disc-shaped members are disposed in sealing relationship with the input port of the second valve means.
 13. The pneumatic system of claim 12 in which only one aperture from each of the pair of disc-shaped members is in alignment.
 14. The pneumatic system of claim 12 in which a first of the pair of disc-shaped members is composed of resilient material, the first disc-shaped member deforming away from the second disc-shaped member when fluid seeks to flow from the second to the first disc-shaped member thereby allowing fluid to flow through all of the apertures in both disc-shaped members, and the first disc-shaped member sealing off the nonaligned apertures when fluid seeks to flow from the first to the second disc-shaped member thereBy allowing fluid to flow through only the aligned apertures in the disc-shaped members.
 15. The pneumatic system of claim 14 in which the total area of the nonaligned apertures is greater than the total area of the aligned apertures thereby making the first time delay greater than the second time delay. 